1. Field of the Invention
The present invention relates to a step screen for conveying solid particles upwards and securely removing them from wastewater flowing through an aqueduct without any special restrictions in the installation condition, and more particularly to an elliptic motion driving apparatus for a step screen, which enables movable plates to move elliptically so that impurities in wastewater may be drawn and securely carried as they stand on each movable plate even though the step screen is installed at an inclination more than 45xc2x0 to the ground of the aqueduct.
2. Description of the Related Art
Generally, a step screen is used to convey and eliminate adulterated things in wastewater flowing through a sewage aqueduct such as a sewage disposal plant or industrial wastewater disposal plant. To carry and remove impurities, the step screen has a plurality of lattice plates which are composed of toothed steps configured a set of stairs at a certain angle. The plates are classified into two types; movable and stationary plates, which are arranged in turn. A movable plate is elevated one step per one cycle so as to convey the caught impurities. Thus, the impurities are screened and conveyed without any dissipation or loss of disintegration from their initially filtered state.
FIG. 1 shows a conventional step screen installed with a common inclination of 45xc2x0 on an aqueduct bottom 10, FIGS. 2 and 3 are front and side views of the conventional step screen, respectively. FIGS. 4 and 5 are a sectional view of a circular motion driving unit 50 and a side view of a driven link 60 for transferring circular motion of the circular motion driving unit 50 to a movable column 45 linked to movable plates 20.
As shown in the figures, the conventional step screen is commonly installed at 45xc2x0 on the aqueduct bottom 10 through which wastewater passes. In the step screen, the movable columns 45 linked to both sides of the circular motion driving unit 50 along fixed frames 40 composing both sides of the screen may circularly move to a longitudinal direction. At the same time, the movable plates 20 arranged inside the fixed frames 40 perform circular movements so that impurities 70 (see FIG. 7) pushed upward onto the next steps of the stationary plates by movable plates 20 may be successively moved upward along the stationary plates by each circular turn of the movable pates.
In other words, the movable plates 20 perform circular movements so that the inclination of the steps of lattice plates (see FIG. 6) has an angle of about 45xc2x0 to a horizontal level of the aqueduct bottom 10. For that reason, as an eccentric rotation cam 51 connected through a power transmission shaft 53 to a driving motor 65 at an upper portion of the screen rotates, the circular motion of the circular motion driving motor 50 is transferred to an eccentric shaft 52. The circular motion of the circular motion driving unit 50 also makes a driven link 60, axially connected to the eccentric shaft 52 through a link bar 61, move in a circular motion. At the same time, the corresponding longitudinal movable column 45 is moved circularly so that the movable plates 20 on the whole may perform in a regular circular motion between each pair of stationary plates 30.
As shown in FIG. 6, in the conventional step screen, the downward portion 21 of each toothed step 20 projected at the side view of the movable plates 20 is perpendicular. Thus, when the screen is inclined to a 45xc2x0 angle to the aqueduct bottom 10, the movable plates 20 of the conventional step screen may push upward and convey impurities 70 in a stable manner while maintaining horizontally the terrace portion 22 of each toothed step 20, whose section is triangularly projected at the longitudinal side view of the movable plates 20, as shown in FIG. 7. However, if the screen is installed at an angle of more than 45xc2x0, the terrace portion 22 of each toothed step 20 inclines downward below the horizontal level. So there still remains a structural difficulty that the screen is not suitable for moving impurities 70 at a steep inclination.
In addition, the conventional step screen in which the movable plates 20 circularly moves at an inclination of 45xc2x0 is effective only at an installation angle of 45xc2x0 to the aqueduct bottom, which requires more setup space than a rake classifier (filter) with an installation angle of 75xc2x0. Even more, when the installation environment requires an incline of more than 45xc2x0 to the screen, the construction design should be changed by a large degree.
Furthermore, the conventional screen supports the movable column 45 only at two points, namely top and bottom, in the circular motion of the movable plates 20. Thus, if there is a large screen requiring a long movable column 45 for a deep aqueduct, the allowable aqueduct depth is limited to 2.7M due to structural limitations. In addition, the method of driving the movable plates 20 in a circular motion also has the problem that the movable plates 20 cannot perform movement proper to push upward the impurities onto the next steps of the stationary when the toothed step is steeply inclined.
The present invention is designed to overcome the structural problems of the prior art caused by the circular motion of the movable plates which maintain a step angle of about 45xc2x0, and an object of the invention is to provide an elliptic motion driving apparatus for a step screen, in which the toothed steps of movable and stationary plates maintain an inclination over 45xc2x0 even when the screen is installed at a steep incline of more than 45xc2x0, so that movable plates having such toothed steps may move elliptically to push upward and convey impurities in wastewater in a stable manner.
In order to accomplish the above object, the present invention provides an elliptic motion driving apparatus for a step screen in which the elliptic motion of an elliptic motion driving unit is transferred to a driven link so as to make steeper movable plates, connected by a movable column, rotate elliptically regularly in a longitudinal direction of the movable column, which includes a driving rotation cam, one end of which is combined to a power transmission shaft rotating in linkage with a worm reduction gear of a driving motor; an eccentric shaft for horizontal motion, axially combined to the other end of the driving rotation cam so that a horizontal eccentric bearing of the eccentric shaft for horizontal motion moves horizontally along a horizontal motion guiding rail as the driving rotation cam rotates; and an eccentric shaft for vertical motion combined to the eccentric shaft for horizontal motion through an eccentric rotation cam so that a vertical eccentric bearing of the eccentric shaft for vertical motion moves vertically along a vertical motion guiding rail as the eccentric shaft for horizontal motion rotates.